Classifications

• • G—PHYSICS
  • G06—COMPUTING; CALCULATING OR COUNTING
  • G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
  • G06K7/00—Methods or arrangements for sensing record carriers, e.g. for reading patterns
  • G06K7/0008—General problems related to the reading of electronic memory record carriers, independent of its reading method, e.g. power transfer
• • G—PHYSICS
  • G06—COMPUTING; CALCULATING OR COUNTING
  • G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
  • G06K7/00—Methods or arrangements for sensing record carriers, e.g. for reading patterns
• • G—PHYSICS
  • G06—COMPUTING; CALCULATING OR COUNTING
  • G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
  • G06K19/00—Record carriers for use with machines and with at least a part designed to carry digital markings
  • G06K19/06—Record carriers for use with machines and with at least a part designed to carry digital markings characterised by the kind of the digital marking, e.g. shape, nature, code
  • G06K19/067—Record carriers with conductive marks, printed circuits or semiconductor circuit elements, e.g. credit or identity cards also with resonating or responding marks without active components
  • G06K19/07—Record carriers with conductive marks, printed circuits or semiconductor circuit elements, e.g. credit or identity cards also with resonating or responding marks without active components with integrated circuit chips
• • G—PHYSICS
  • G06—COMPUTING; CALCULATING OR COUNTING
  • G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
  • G06K7/00—Methods or arrangements for sensing record carriers, e.g. for reading patterns
  • G06K7/10—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation
  • G06K7/10009—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation sensing by radiation using wavelengths larger than 0.1 mm, e.g. radio-waves or microwaves
  • G06K7/10316—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation sensing by radiation using wavelengths larger than 0.1 mm, e.g. radio-waves or microwaves using at least one antenna particularly designed for interrogating the wireless record carriers
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
  • H04B1/02—Transmitters
  • H04B1/04—Circuits
  • H04B1/0458—Arrangements for matching and coupling between power amplifier and antenna or between amplifying stages
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
  • H04B1/38—Transceivers, i.e. devices in which transmitter and receiver form a structural unit and in which at least one part is used for functions of transmitting and receiving
  • H04B1/40—Circuits
  • H04B1/50—Circuits using different frequencies for the two directions of communication
  • H04B1/52—Hybrid arrangements, i.e. arrangements for transition from single-path two-direction transmission to single-direction transmission on each of two paths or vice versa
  • H04B1/525—Hybrid arrangements, i.e. arrangements for transition from single-path two-direction transmission to single-direction transmission on each of two paths or vice versa with means for reducing leakage of transmitter signal into the receiver
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
  • H04B1/38—Transceivers, i.e. devices in which transmitter and receiver form a structural unit and in which at least one part is used for functions of transmitting and receiving
  • H04B1/40—Circuits
  • H04B1/54—Circuits using the same frequency for two directions of communication
  • H04B1/56—Circuits using the same frequency for two directions of communication with provision for simultaneous communication in two directions

Definitions

• the invention relates to compensating an antenna mismatch in a radio frequency identification reader.
• Radio Frequency Identification is a technology that incorporates the use of electromagnetic or electrostatic coupling in the radio frequency spectrum to identify objects having RFID tags affixed thereto.
• RFID systems in general provide the advantage of not requiring direct contact or line-of-sight scanning.
• a typical RFID system includes an RFID reader and a plurality of RFID tags that are affixed to the objects of interest.
• Each RFID reader includes an antenna and a transceiver.
• An RFID reader uses the antenna and transceiver to transmit radio frequency signals to the RFID tag.
• the tag transmits data back to the reader by modulating a signal that is received at the RFID reader antenna.
• tags use variable impedance coupled to the antenna that can be used to change the amount of energy that is reflected back by the tag. These tags can transmit data to the reader by selectively varying the impedance to modulate the backscattered signals. As such, RFID tags can be used to identify and track large numbers of objects. Furthermore, because RFID tags are relatively low-cost components, they have the ability to track large numbers of objects at relatively low costs.
• FIG. 1 illustrates an example of an RFID reader 100.
• the RFID reader 100 comprises a transmission circuit 102 to enable transmission of ra- dio signals to an RFID tag 122. Additionally, the RFID reader 100 comprises a reception circuit 106 to enable reception of radio signals transmitted from the RFID tag 122.
• an RFID reader comprises one antenna 110 to be used in both transmission and reception in order to reduce the physical size of the reader.
• the signals to be transmitted are directed from a transmission circuit 102 of the reader to the antenna 110 through a circulator 104.
• the same circulator 104 conveys signals received through the antenna 110 to a reception circuit 106 of the RFID reader 100.
• the circulator 104 is not an ideal component and, therefore, components of the transmitted signal may leak to the reception circuit 106.
• the antenna of the reader may be broken or disconnected from the antenna port occasionally. This results in a severe mismatch in the antenna port and almost a total reflection of the transmitted signal. A high-level transmission signal reflected back to the reception circuit of the reader typically breaks the reception circuit. It would be advantageous to find a solution to prevent the breakdown of the reception circuit in such cases.
• Patent publication WO2006037241 discloses a solution for compensating the interference caused by a transmitter of an RFID reader to a receiver of the reader.
• a correction signal is generated with a digital signal processor, and the correction signal is fed to the receiver through a digital-to-analog (D/A) converter and a linear modulator. Accordingly, the interfering signal is compensated for in the receiver.
• the disclosed solution is not cost-effective due to additional, high-cost components included in the reader.
• the disclosed solution requires an additional signal processing, an additional D/A converter, and an additional modulator in order to create the correction signal and implement in- terference compensation. These additional components increase the cost of the RFID reader considerably.
• An object of the invention is to provide an improved solution for compensating the effects of a transmitted signal leaking to a reception circuit of a radio frequency identification reader.
• a component mismatch compensation method in a radio frequency identification (RFID) reader comprises transmitting a first signal to an antenna port of the RFID reader, creating a compensation signal on the basis of knowledge of signal components of the transmitted first signal leaking to a receiver side of the RFID reader, and combining the compensation signal with a second signal received from the antenna port in order to suppress the signal components of the first signal from the received second signal.
• the method further comprises directing the first signal also to a compensation circuit and creating the compensation signal by modifying the first signal in the compensation circuit.
• a radio frequency identification (RFID) reader comprising a transmission circuit configured to generate radio frequency signals for transmission, a coupling unit configured to couple signals to be transmitted from the transmission circuit to an antenna port of the RFID reader, and a compensation circuit configured to create a compensation signal on the basis of knowledge of signal components of a transmitted signal leaking to a receiver side of the RFID reader and combine the compensation signal with a signal received from the antenna port.
• the coupling unit is configured to couple the signal transmitted from the transmission circuit also to the compensation circuit, and the compensation circuit is configured to create the compensation signal by modifying the signal.
• a computer program product encoding a computer program of instructions for executing a computer process for component mismatch compensation in a radio frequency identification (RFID) reader.
• the process comprises transmit- ting a first signal to an antenna port of the RFID reader, configuring a compensation circuit of the RFID reader to create a compensation signal on the basis of knowledge of signal components of the transmitted first signal leaking to a receiver side of the RFID reader, and configuring the compensation circuit to create the compensation signal by modifying the first signal directed also to the compensation circuit.
• RFID radio frequency identification
• the invention provides a simplified structure for the creation of the compensation signal.
• the signal to be transmitted may be utilized in the creation of the compensation signal and, thus, no separate signal generator is necessary for the creation of the compensation signal.
• Figure 1 illustrates a block diagram of an RFID reader and an RFID tag
• Figure 2 illustrates the structure of an RFID reader according to an embodiment of the invention
• Figure 3 illustrates a detailed block diagram of the RFID reader comprising a compensation circuit according to an embodiment of the invention
• FIG. 4 illustrates a block diagram of the RFID reader according to another embodiment of the invention.
• Figure 5 is a flow diagram illustrating a process for component mismatch compensation in the RFID reader according to an embodiment of the invention.
• RFID radio frequency identification
• the RFID reader 200 comprises a transmission/reception circuitry 208 to enable transmission and reception of radio signals.
• the transmission/reception circuitry 208 may be operationally divided into a transmission circuit and a reception circuit.
• the transmission circuit carries out operations necessary to convert signals to be transmitted into a format suitable for transmission.
• the transmission circuit may perform upconversion, amplification, and filtering procedures to a signal to be transmitted.
• the reception circuit carries out operations necessary to convert received signals into a format suitable for data detection.
• the reception circuit may perform downcon- version, amplification, and filtering procedures to a received signal and then forward it to an analog-to-digital converter for further processing.
• the trans- mission/reception circuitry 208 may utilize a single antenna for both transmission and reception of radio signals.
• the RFID reader 200 further comprises a processing unit 204 controlling the operations carried out in the RFID reader 200.
• the processing unit 204 may control the transmission and reception of signals transmitted or re- ceived through the transmission/reception circuitry 208.
• the processing unit 204 may also control the operation of other components of the RFID reader 204.
• the processing unit 204 may be implemented by a digital signal processor with suitable software embedded in a computer readable medium, or by separate logic circuits, for example with ASIC (Application Specific Integrated Circuit).
• the RFID reader 200 further comprises a memory unit 206 storing information and parameters necessary for the operation of the RFID reader
• the memory unit 206 may store instructions for the processing unit 204 and parameters required in transmission and/or reception of signals to/from the RFID reader 200.
• the RFID reader 200 may further comprise a user interface 202 for communication between the RFID reader 200 and a user of the RFID reader 200.
• the user interface 202 may comprise a display unit and an input device, for example.
• the RFID reader 200 communicates with an RFID tag 220 through a wireless radio link.
• the RFID tag comprises a transmission/reception circuitry 222 and a memory unit 224.
• the transmission/reception circuitry is configured to receive a given radio signal transmitted from the RFID reader 200, modulate the received radio signal with information stored in the memory unit 224, and transmit the modulated signal back to the RFID reader 200 to carry out the radio frequency identification.
• the RFID tag 220 may respond only to a specific activation signal received from the RFID reader.
• the RFID tag 220 may be configured not to respond to them.
• the RFID tag comprises no energy source and, thus, the energy necessary for the operation of the RFID tag 220 is obtained from the received signal.
• the RFID reader 200 may also transmit additional energy bursts to provide the RFID tag 220 with enough energy.
• FIG. 3 illustrates a detailed block diagram of the RFID reader 200 according to an embodiment of the invention.
• a processing unit 204 is the same as described above with reference to Figure 2.
• the processing unit 204 transmits signals through a transmission circuit 302 to an antenna port 330.
• a digital-to-analog (D/A) converter 322 may be provided between the processing unit 204 and the transmission circuit 302.
• the transmission circuit 302 processes an information signal to be transmitted into a radio frequency signal.
• the transmission circuit 302 may perform the same operations as the transmission circuit described above.
• the transmission circuit 302 then outputs the radio frequency signal to the antenna port 330 through a circulator 306.
• the circulator 306 conveys signals received from the transmission circuit 302 to an antenna connected to the antenna port 330 and signals re- ceived from the antenna port 330 to a reception circuit 310.
• the reception circuit 310 may perform the same operations as the reception circuit described above.
• the reception circuit 310 then outputs the signals to the processing unit 204 through an analog-to-digital (A/D) converter 320.
• A/D analog-to-digital
• the circulator 306 may not be an ideal component and components of the transmitted signals may leak to the reception cir- cuit 310, thereby degrading the performance of data detection.
• the RFID reader 200 may first send a data signal to the RFID tag 220 and then energy bursts to provide the RFID tag 220 with energy so that the RFID tag 220 may create a response signal to the data signal received from the reader 200. Consequently, the RFID reader 200 receives the response signal from the RFID tag 220 while transmitting the energy bursts, and components of the transmitted signal (the energy bursts) leak to the receiver side of the reader 200 while receiving the response signal from the tag 220. This may be a problem particularly in RFID readers utilizing the same antenna for simultaneous transmission and reception.
• a signal is being transmitted while another signal is being re- ceived, components of the transmitted signals leak to the reception circuit 310 degrading the performance of detection of the received signal. Additionally, there may be antenna mismatches between the antenna port and the antenna, which results is reflection of a portion of the transmitted signal from the antenna port. These signal components are also conveyed to the reception circuit 310 through the circulator 306.
• the RFID reader 200 includes a compensation circuit 340.
• the signal output from the transmission circuit 302 may be conveyed to the circulator 306 through a cou- pling unit 304.
• the coupling unit 304 may be a directional coupler which is configured to convey the signal received from the transmission circuit 302 not only to the circulator 306 but also to the compensation circuit 340.
• the compensation circuit 340 comprises an amplitude adjustment unit 312 and a phase adjustment unit 314 which modify the amplitude and the phase of the input signal (the signal received from the transmission circuit 302 through the coupling unit 304).
• the amplitude adjustment unit 312 and the phase adjustment unit 314 may be implemented by a vector modulator, for example.
• the operation of the compensation circuit 340 is controlled by the processing unit 204 which provides the amplitude adjustment unit 312 with an am- plitude parameter value and the phase adjustment unit 314 with a phase parameter value.
• the parameters define the amount of amplitude and phase ad- justment of the input signal.
• the processing unit 204 may provide the adjustment units 312 and 314 with parameter values through D/A converters 316 and 318, respectively.
• the purpose of the compensation circuit 340 is to create a compensation signal which suppresses the transmitted signal leaking to the reception circuit, when these signals are combined.
• the compensation circuit 340 comprises also a combiner 308 which combines the signal received from the antenna port 330 through the circulator 306 with the compensation signal, and outputs the resulting signal to the reception circuit 310. Accordingly, the combiner 308 may be located between the circulator 306 and the reception circuit 310.
• the amplitude of the signal received through the coupling unit 304 may be modified before the phase adjustment, or vice versa.
• the signal received through the coupling unit 304 may be divided into two signals. One of the two signals may be input to the amplitude adjustment unit 312 and the other to the phase adjustment unit 314. The outputs of the amplitude adjustment unit 312 and the phase adjustment unit 314 may then be combined, e.g. summed together.
• the processing unit 204 provides the amplitude adjustment unit 312 and the phase adjustment unit 314 with parameter values on the basis of knowledge of signal components of the transmitted signal leaking to the reception circuit 310. On the basis of this knowledge, the processing unit 204 may select an optimal parameter value combination to suppress the leaking components of the transmitted signal.
• the knowledge of the signal components of the transmitted signal leaking to a reception circuit 310 may be obtained by transmitting a test signal to the antenna port 330 during a testing phase when no data transmission and reception is carried out. Accordingly, the processing unit 204 transmits a test signal to the antenna port 330 through the transmission circuit 302, the coupling unit 304, and the circulator 306. The coupling unit 304 directs the test signal also to the compensation circuit 340. Components of the test signal leak through the circulator 306 and reflect from the antenna port 330 to the combiner 308 of the compensation circuit 340.
• the processing unit 204 provides the amplitude adjustment unit 312 and the phase adjustment unit 314 with different amplitude and phase shift parameter value combinations and monitors the level of the signal it receives through the reception circuit 310 and the A/D- converter 320.
• the idea is to create a compensation signal which suppresses the leaking signal components completely, i.e. that the signal level obtained as an output of the combiner 308 is as low as possible.
• the amplitude and phase shift parameter value combinations may be pre-determined and stored in the memory unit 206 of the RFID reader.
• the modification of the test signal with different amplitude and phase shift parameter value combinations in the compensation circuit 340 results in different modifications of the test signal and a different residual signal, when the modified test signal is combined with the signal received from the circulator.
• the combining is carried out in the com- biner 308 which may be a summation unit, for example.
• the residual signal obtained as an output of the combiner 308 is fed to the processing unit 204 through the reception circuit 310 and the A/D converter 320.
• the processing unit 204 measures the level of the residual signal, provides the compensation circuit 340 with a different amplitude and phase shift parameter value combina- tion and measures the level of the resulting residual (or combined) signal.
• the processing unit 204 may measure another property, such as the power, of the residual signal. Accordingly, the processing unit 204 measures the levels of the residual signals resulting in the modification of the test signal with different amplitude and phase shift parameter value combinations, and selects the parameter combination which results in the lowest level of the residual signal.
• the lowest level indicates that the compensation signal providing the lowest level is the most optimal for suppressing the signal components leaking through the circulator and/or reflecting back from the antenna port 330.
• the compensation signal has the same amplitude as the test signal leaking from the transmitter side to the receiver side and opposite phase.
• the processing unit 204 selects the amplitude and phase shift parameter value combination resulting in the most optimal compensation signal to be used when transmitting and receiving information signals at the RFID reader 200. If the RFID reader 200 comprises multiple antenna ports, the testing phase may be carried out for each of the multiple antenna ports. Accordingly, the test signal may be transmitted to each antenna port and a compensation signal may be generated for each antenna port according to the procedure described above.
• the parameters of the compensation signal associated with each antenna port may be stored in the memory unit 206, and loaded from the memory unit 206 when data transmission starts. The loaded parameters then define the compensation signal to be used in the data transmission.
• the antenna ports may have a similar structure and similar components, mismatches at the antenna ports may differ. Accordingly, it may be advantageous to create a unique compensation signal for each antenna port.
• the RFID reader 200 may further optimize the parameters (amplitude and/or phase shift parameter) of the compensation signal.
• the processing unit 204 may initiate a parameter optimization procedure according to a determined criterion. For example, the parameter optimization procedure may be carried out at pre-determined time instants dur- ing the data transmission.
• the processing unit 204 may provide the compensation circuit 340 with different parameters than those determined during the testing phase and monitor the effect of the new parameters to data reception.
• the new parameters may have values close to those determined during the testing phase.
• Monitoring the ef- fects may comprise monitoring the number of successful read events. If the number of successful read events is higher with the new parameters than with those determined during the testing phase, the processing unit 204 may keep the new parameters. On the other hand, if the number of successful read events is lower with the new parameters, the processing unit 204 may discard the new parameters and revert to the old parameters.
• the advantage of optimizing the parameters of the compensation signal during the data transmission is to compensate for the changes in component properties caused by changes in temperature, for example.
• the use of the compensation circuit 340 according to an embodi- ment of the invention is particularly advantageous in situations where signal transmission and reception are performed simultaneously.
• the advantages gained with the compensation circuit 340 are not, however, limited to this.
• the above-described proce- dure may be used to suppress the external interfering signal component.
• the above-described procedure of creating the compensation signal may be used to suppress the strongest signal interfering the reception of a desired data signal. If multiple interfering signals are present, a plurality of amplitude and phase adjustment unit pairs may be concatenated, each pair sup- pressing one interfering signal.
• the test signal may be transmitted to the antenna port with a lower power level than that used for transmitting an actual data signal. Therefore, the testing phase may also be utilized for determining, whether or not there is a properly functioning antenna connected to the antenna port. When there is no antenna connected to the antenna port, or when the antenna is broken, there is a severe mismatch in the antenna port and the test signal reflects back almost completely. On the other hand, if there is a properly functioning antenna connected to the antenna port, only a small portion of the transmitted test signal reflects back from the antenna port.
• Figure 4 illustrates a structure for determining, whether or not there is a properly functioning antenna connected to a plurality of antenna ports 330, 332, and 334 of an RFID reader according to an embodiment of the invention.
• FIG. 4 is a simplified block diagram illustrating only the components that are relevant for the description.
• a switching mechanism 400 operated by the processing unit 204 is provided between the circulator 306 and the antenna ports 330 to 334.
• the processing unit 204 controls the switching mechanism 400 in order to select an antenna port 330, 332, or 334 to which a signal is to be transmitted. That is, the processing unit 204 controls the switching mechanism to connect the transmission circuit 302 (through the circulator 306) to a selected antenna port 330, 332, or 334.
• the processing unit 204 may transmit a test signal to each of the antenna ports 330, 332, and 334, and monitors the level of a signal reflected back from the antenna ports 330, 332, and 334 through the circulator 306 and the reception circuit 310 in order to determine which of the antenna ports 330, 332, and 334 has a properly functioning antenna connected thereto.
• the processing unit 204 may control the switching mechanism 400 to connect the transmission circuit 302 to each of the antenna ports 330, 332, and 334 at a time so that each antenna port is tested separately.
• the processing unit 204 may first control the switching mechanism 400 to connect the transmission circuit 302 to a first antenna port 330, transmit a test signal to the first antenna port 330 through the transmission circuit 302, receive a reflected signal component through the reception circuit 310 and measure the level of the received signal.
• the test signal may the same test signal as that described above with ref- erence to Figure 3. If the measured level of the received signal exceeds a predetermined threshold, the processing unit 204 determines that there is no properly working (or functioning) antenna connected to the first antenna port 330. On the other hand, if the measured level of the received signal is lower than the threshold, the processing unit 204 determines that there is a properly functioning antenna connected to the first antenna port 330.
• the processing unit 204 may select the antenna port (or ports) for the actual data transmission. Accordingly, the processing unit 204 may transmit, through the transmission circuit 302, a data sig- nal to the antenna port(s) having a properly functioning antenna connected thereto, and prevent the transmission of the data signal to the antenna ports not having a properly functioning antenna connected thereto. This may be carried out by controlling the switching mechanism 400 to connect the transmission circuit 302 to the antenna port(s) having a properly functioning antenna connected thereto. If no antenna port is determined to be connected to a properly functioning antenna, the processing unit 204 may prevent the transmission of the data signal to every antenna port.
• the embodiment of the invention described above transmits a low-power test signal to the antenna ports during a testing phase in order to detect the antenna ports not connected to a properly functioning antenna and prevent transmission of a high-power data signal to those antenna ports.
• the testing phase may be carried out periodically between the transmissions of data signals. This solution prevents the breakdown of the reception circuit, if an antenna is accidentally removed from an antenna port or if it has broken.
• the RFID reader may inform the user of the reader of a malfunction in an antenna port through the user interface of the RFID reader. Alternatively, the RFID reader may report the malfunction to another instance, for example to a host system communicating with the RFID reader.
• the present solution enables switching of an antenna on the fly. For example, if an antenna connected to an antenna port of the RFID reader is replaced with another antenna, the replacement may be carried out while the RFID reader is powered up or even transmitting.
• this automated checking of an- tenna port connections enables additionally that an antenna of one type may replaced with an antenna of another type without degrading the performance of the detection of received signals. If the antenna is replaced with another type of antenna, there may be a mismatch between the antenna port and the antenna of the new type, which results in stronger reflecting components of a signal transmitted to the antenna port.
• the compensation circuit 340 is now used to suppress these components reflecting back to the reception circuit, thus eliminating the degrading effects to the data reception. Accordingly, the RFID reader according to an embodiment of the invention automatically adapts to the new type of antenna, and no separate testing and antenna tuning arrangements are necessary.
• FIG. 5 is a flow diagram illustrating a process for component mismatch compensation in an RFID reader according to an embodiment of the invention.
• the RFID reader may employ a single antenna for simultaneous transmission and reception. Accordingly, transmitted and received signals are conveyed through a circulator. The process starts in block 500.
• a test signal is transmitted to one or more of the antenna ports of the RFID reader during a testing phase. Since the components of the RFID reader are not ideal and there may be a mismatch at the one or more antenna ports, components of the transmitted signal leak to a reception circuit of the RFID reader. These leaking signal components of the transmitted test signal are received in block 504.
• a compensation signal is created on the basis of the signal components received from the selected antenna port.
• the compensation signal may be created by directing the test signal transmitted to the selected antenna port also to a compensation circuit which modifies the test signal in order to create a compensation signal to suppress the components of the test signal leaking to the receiver side.
• the compensation signal may be created by modifying amplitude and phase of the test signal in the compensation circuit, combining the modified test signal with the components of the test signal leaking to the receiver side, and measuring the level of the combined residual signal. This may be carried out with different amplitude and phase shift modifications, and amplitude and phase shift parameters providing a compensation signal suppressing the components of the test signal leaking to the receiver side the most may be selected.
• a first data signal and energy bursts may be transmitted to the selected antenna port and also to the compensation circuit in step 510.
• a second data signal may be received from an RFID tag, to which the first data signal was transmitted in step 510, while transmitting the energy bursts.
• Components of the signals leaking to the receiver side may be suppressed with a compensation signal created by modifying the signal directed to the compensation circuit with the selected amplitude and phase shift parameters in block 512.
• the compensation signal and the received second data signal may then be combined in block 514 in order to remove the leaking component from the received second signal. Then, the received second data signal may be detected in block 516.
• the parameters of the compensation signal are optimized.
• the optimization may be carried out by changing the parameters and monitoring the effect in the quality of data reception.
• the new parame- ters may be around those determined during the testing phase. If the use of the new parameters results in a better reception quality, the new parameters are maintained. Otherwise, the new parameters are discarded and the parameters determined during the testing phase are restored.
• the optimization may be carried out for every antenna port of the RFID reader during deter- mined optimization intervals.
• block 520 it is determined whether or not to carry out another testing phase in order to modify the parameters used in creation of the compensation signal and to recheck the antenna ports. If it is determined, that the testing phase is to be carried out, the process returns to block 502 for another testing phase. Otherwise, the process returns to block 510 for transmission of another data signal.
• the embodiments of the invention may be realized in an RFID reader comprising a transmission circuit, a reception circuit, a compensation circuit, and a processing unit operationally connected to the transmission, re- ception and compensation circuits.
• the processing unit may be configured to perform at least some of the steps described in connection with the flowchart of Figure 5 and in connection with Figures 3 and 4.
• the embodiments may be implemented as a computer program comprising instructions for executing a computer process for component mismatch compensation in the RFID reader.
• the computer program may be stored on a computer program dis- tribution medium readable by a computer or a processor.
• the computer program medium may be, for example but not limited to, an electric, magnetic, optical, infrared or semiconductor system, device or transmission medium.
• the computer program medium may include at least one of the following media: a computer readable medium, a program storage medium, a record medium, a computer readable memory, a random access memory, an erasable programmable read-only memory, a computer readable software distribution package, a computer readable signal, a computer readable telecommunications signal, computer readable printed matter, and a computer readable compressed software package.

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Cited By (4)

Citations (8)

• 2006
  • 2006-08-24 FI FI20065527A patent/FI119083B/sv not_active IP Right Cessation
• 2007
  • 2007-08-22 WO PCT/FI2007/050453 patent/WO2008023096A1/en active Application Filing

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